1. Field of the Invention
The present invention relates to video transcoding and, more specifically but not exclusively, to changing spatial resolution in encoded video bit-streams.
2. Description of the Related Art
This section introduces aspects that may help facilitate a better understanding of the invention(s). Accordingly, the statements of this section are to be read in this light and are not to be understood as admissions about what is in the prior art or what is not in the prior art.
Video transcoding is a process of converting a previously encoded video bit-stream into another encoded video bit-stream, e.g., with a different bit rate, a different frame rate, a different display format, and/or a different coding method. For example, video transcoding can be used to convert a video bit-stream encoded in one standard into a video bit-stream encoded in a different standard, with the initial and final standards selected from a set consisting of the H.26x and MPEG-z families of standards, where x=1, 3, 4 and z=1, 2, 4. Another important example of video transcoding is conversion of an encoded video bit-stream having one spatial resolution into an encoded video bit-stream having a different (typically lower) spatial resolution, without changing the standard. Other video-transcoding operations may include adding enhanced error resilience, inserting logos and watermarks, adjusting temporal resolution, etc. Video transcoding advantageously enables multimedia devices of diverse formats and capabilities to exchange video content on heterogeneous transport-network platforms, such as the Internet.
The H.26x and MPEG-z families of standards employ motion estimation to compress video data based on temporal redundancy present in successive frames. To achieve good video quality with a significant degree of compression, a video encoder typically performs an exhaustive search, during which the encoder attempts to find a block in a reference (past or future) frame that best matches a given block in the current frame, e.g., by maximizing a cross-correlation function or minimizing an error criterion. This search makes the motion-estimation algorithmic module one of the dominant components of a video transcoder in terms of computational complexity and processor load. It is therefore desirable to have a motion-estimation algorithm that can produce acceptable video quality while keeping the corresponding computational complexity and/or processor load at relatively low levels.